CN107194102B - Series voltage balancing method for high-voltage flexible direct-current converter valve supporting insulator - Google Patents
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Abstract
The invention discloses a method for balancing series voltage of a high-voltage flexible direct-current converter valve supporting insulator, belonging to the field of electric field algorithms of converter valves. The method comprises two steps of selecting a waterway clamping point and optimizing the effect of circuit equivalent calculation. The metal parts connected with the water path and the insulator string are mutually constrained, and through the characteristics that the water path potential is uniformly distributed and the reactance value of the water path resistance value is smaller than that of the capacitor, the phenomenon of uneven potential distribution caused by uneven distribution of the stray capacitor is directly and quickly improved, the principle is simple and understandable, the self structural characteristics are well utilized, an additional structure is not required to be added, the engineering requirement can be well met, the installation cost is low, and the engineering implementation is convenient. And in order to calculate the optimization result more conveniently, a circuit equivalent calculation method is adopted for calculation, so that the position of the clamping point is conveniently and repeatedly modified, and the optimal optimization scheme is searched. The circuit parameter calculation is carried out through the equivalent resistance capacitance value, the calculation is simple, the calculation time is short, and the engineering cost and the time can be greatly saved.
Description
Technical Field
The invention belongs to the field of electric field algorithms of converter valves, and particularly relates to a series voltage balancing method for a high-voltage flexible direct-current converter valve supporting insulator.
Background
While traditional extra-high voltage direct current transmission is developed, a flexible direct current transmission technology based on a voltage source converter is also continuously developed. In the operation from south Hui, Zhoushan, south Australia, Xiamen to Luxi projects, the voltage level is continuously improved from +/-30 kV to +/-800 kV, the structure of the converter valve is also greatly changed, and the insulator plays an important role in supporting and insulating and becomes a key concern object. When the working voltage is increased, the single insulator support cannot meet the engineering requirement, and the plurality of insulators are connected into an insulator string by simple machinery to form a necessary trend. Under the action of alternating voltage, stray capacitance exists between the metal part of the insulator string and other conductors, so that the voltage distribution along the insulator string is uneven, the higher the voltage difference borne by the insulator which is closer to a high-voltage end is, the higher the borne voltage is, insulation flashover, corona, deterioration and the like are easily caused. Therefore, the insulator string voltage equalizing design is receiving more and more attention.
At present, a lot of researches are carried out on voltage equalization methods of insulator strings of alternating-current and direct-current lines, and related researches on insulators for converter valves are few, but as the voltage grades are continuously increased, the insulator strings are gradually lengthened, the voltage grades are higher, the number of the insulators connected in series is more, the voltage distribution is more uneven, the requirements on voltage equalization design of the insulator strings of the converter valves are stricter, and the method becomes a key for realizing insulation optimization design of the converter valves under small safety margins.
The voltage distribution of the insulator strings is related to the type of the insulator, the arrangement of the shielding rings and the selection of a hardware structure, the voltage-sharing optimization method of the insulator strings in the current converter valve tower is basically a reference line optimization method, and two voltage-sharing optimization schemes are generally adopted, wherein one optimization scheme is that the insulators with different characteristics are serially connected, for example, large-capacitance and large-creepage-distance insulators are adopted at the two ends of the insulator strings, and the middle part of the insulator strings is still made of common insulators to form a flower-inserting insulator string. The method is complex to implement, large in structural change and complex in model selection. The second optimization scheme is that the end part of the insulator is additionally provided with the equalizing ring, the corona starting voltage and the flashover voltage of the insulator are improved by additionally arranging the equalizing ring, the earth capacitance of the insulator is increased, the voltage distribution of the insulator string is improved, and the cost is low. However, the size and the installation position of the grading ring need repeated numerical calculation and modeling simulation, the modification period is long, and the optimal position is not well determined. The above method often ignores the characteristics of the converter valve in the structure, as shown in fig. 1, a plurality of inlet and outlet cooling water pipes are arranged in the converter valve tower, the potential distribution of the inlet and outlet cooling water pipes is affected by the conductivity, which is equivalent to a resistance with a very large value, and the whole potential is uniformly and linearly distributed. In the converter valve, the water pipe becomes a pressure equalizing means which is very convenient to adopt.
The water way and the flange of the connecting part of the series insulator are connected together by metal for equipotential treatment, and the method is called water way clamping. The waterway clamping is a method for solving the problem of uneven voltage distribution of the insulator string, and an optimization method of the waterway clamping is not adopted by engineering at present. The waterway clamping method has small installation difficulty and convenient implementation, and is a non-negligible optimization method.
In the aspect of calculation, methods are more, and due to the advantages of accurate calculation, strong applicability and the like of the finite element method, particularly due to the continuous maturity and development of ANSYS software in the aspect of electric field calculation, a large number of researchers use the finite element method to calculate the electric field of the ANSYS software more. However, considering the coupling of the current field and the electrostatic field after the waterway is clamped, the valve model becomes a quasi-static electric field model, the difficulty of directly analyzing the quasi-static electric field is high, and the realization in ANSYS software is difficult. And in order to obtain a better optimization effect, a circuit equivalent calculation method is adopted to calculate an optimization result, so that the method is more suitable for the engineering requirements of repeatedly modifying the position of the clamping point and searching an optimal optimization scheme. The circuit parameter calculation is carried out through the equivalent resistance capacitance value, the calculation is simple, the calculation time is short, and the engineering cost and time can be greatly saved.
Disclosure of Invention
The invention aims to provide a method for balancing the series voltage of supporting insulators of a high-voltage flexible direct-current converter valve, which is characterized in that while the voltage class of the voltage source converter-based flexible direct-current transmission technology is continuously improved from +/-30 kV to +/-800 kV, the structure of the converter valve is greatly changed, the insulators playing supporting and insulating roles have higher working voltage, and a single insulator support cannot meet engineering requirements, but only a plurality of insulators are simply connected mechanically to form an insulator string to solve the problem; under the action of alternating voltage, stray capacitance exists between the metal part of the insulator string and other conductors, so that the voltage distribution along the insulator string is uneven, and the insulator closer to a high-voltage end bears higher voltage difference, and the insulator bears overhigh voltage, thus easily causing insulation flashover, corona and deterioration; stray capacitance exists between the metal part of the insulator string and the surrounding conductors, which is the most main reason for the unbalanced voltage distribution; actually, a plurality of inlet and outlet cooling water pipes are arranged in the converter valve tower, the potential distribution of the inlet and outlet cooling water pipes is influenced by the electric conductivity, which is equivalent to a resistance with a great numerical value, and the integral potential is uniformly and linearly distributed. In the converter valve, a water pipe becomes a pressure equalizing means which is very convenient to adopt; the water path clamping method is characterized in that a connection point with a metal part of an insulator string is additionally arranged on a water pipe, and a natural voltage division result of a stray capacitor is influenced through a large resistance and a uniform linear voltage distribution characteristic of a water path, so that the purpose of voltage balance is achieved;
three types of stray capacitors C are formed by the metal part provided with the insulator string and the surrounding conductors1、C2And C3(as shown in FIG. 1); wherein C is1Is the stray capacitance between the shield, the valve module and the middle layer metal, C2Is the stray capacitance between the middle layer metal and the grounding base C3Is the stray capacitance between the shield, the valve module and the grounded base. The potential distribution on the insulator string is uneven due to the difference between the existence of the three stray capacitances and the numerical value;
the water path before clamping can be equivalent to a resistor R with extremely large resistance value and a resistor C1、C2、C3After a clamping point connected with the metal part of the insulator is added on the water pipe, the circuit equivalent (the circuit diagram is shown in figure 3) is R1Is a resistance, R, at the upper section of the clamping point of the water path2Is the resistance of the lower section of the waterway clamping point; the valve tower model is equivalent to two capacitors connected in series and two resistors connected in series, and then the two groups of components are connected in parallel; the potential of the water path is linearly distributed under the current field, the resistance value of the water path is smaller than the reactance value of the capacitor, and the clamping point can be changed
And
more closely, the voltage distribution is uniform, and then the problem of uneven voltage distribution caused by stray capacitance is effectively solved by water path clamping; the method specifically comprises the two steps of selecting waterway clamping points and calculating an optimization effect, wherein the optimal clamping point position is repeatedly selected according to the positions of the clamping points; the optimization effect calculation currently and generally adopts finite element electric field calculation: firstly, selecting a proper waterway clamping point, considering the position of a water pipe which is close to the metal part connected with the insulator string as far as possible, repeatedly selecting and optimizing the waterway clamping point, and corresponding to different clamping points, wherein different waterway resistances and different voltage distribution results are obtained. The water pipe is distributed according to the resistance under the current field, affects the partial pressure with the combined action of the capacitance, and is calculated according to the formula (1-1),
R＝L/(γ×A) (1-1)
wherein:
l: the length of the water pipe;
γ: the electrical conductivity of the water;
a: the cross-sectional area of the water tube;
secondly, obtaining the electrostatic energy of the whole valve hall through the numerical calculation function of ANSYS, thereby obtaining the stray capacitance of each part; after obtaining each circuit parameter, the valve tower model is equivalent to a plurality of capacitors connected in series and a plurality of resistors connected in series, the two component devices are connected in parallel, the voltage distribution result of the series insulator after the water channel is clamped is obtained, and the best optimization result is obtained by repeatedly modifying the position of the clamping point and repeatedly calculating.
The invention has the beneficial effects that:
the method for clamping the water channel can directly and quickly improve the phenomenon of uneven potential distribution caused by uneven distribution of stray capacitance by the characteristics that the potential of the water channel is uniformly distributed and the resistance value of the water channel is smaller than the reactance value of a capacitor through potential clamping, has simple and understandable principle, excellently utilizes the structural characteristics of the water channel, does not need to increase an additional structure, can well meet engineering requirements, is quick in calculation, small in installation cost and convenient in engineering implementation, and has higher actual engineering value.
And secondly, the adopted circuit calculation method is simple and rapid, compared with other calculation methods, the model is not required to be repeatedly modified, a large amount of finite element calculation is carried out, the clamping point position can be repeatedly adjusted through simple parameter calculation to obtain the optimal clamping point position, the required voltage-sharing effect is achieved, the engineering difficulty is small, the calculation time is short, and the engineering cost and time are greatly saved.
Drawings
Fig. 1 is a schematic diagram of voltage unevenness of an insulator string.
FIG. 2 is an equivalent circuit diagram of the converter valve tower before water path clamping.
Fig. 3(a, b) are equivalent circuit diagrams before the water channel of the converter valve tower is clamped.
FIG. 4 is a simplified structure diagram of a +/-800 kV converter valve tower model.
FIG. 5 is a schematic diagram of a potential clamping point.
Fig. 6 is a curve of the partial pressure percentage of the lower insulator corresponding to different clamping points under ac/dc withstand voltage.
Detailed Description
The invention provides a voltage distribution balancing method for high-voltage flexible direct converter valve series insulators, which is suitable for the problem of balancing the series voltage of the converter valve tower insulators. While the voltage class of the flexible direct-current transmission technology based on the voltage source converter is continuously improved from +/-30 kV to +/-800 kV, the structure of the converter valve is greatly changed, and because the working voltage of the insulator playing the supporting and insulating role is increased, the single insulator supports the insulator string, the engineering requirements cannot be met, and only a plurality of insulators are connected by simple machinery to form the insulator string; under the action of alternating voltage, stray capacitance exists between the metal part of the insulator string and other conductors, so that the voltage distribution along the insulator string is uneven, and the insulator closer to a high-voltage end bears higher voltage difference, and the insulator bears overhigh voltage, thus easily causing insulation flashover, corona and deterioration; the stray capacitance between the metallic parts of the insulator string and the surrounding conductors is the most dominant cause of the voltage distribution imbalance. The embodiments are described in detail below with reference to the accompanying drawings.
Actually, a plurality of inlet and outlet cooling water pipes are arranged in the converter valve tower, the potential distribution of the inlet and outlet cooling water pipes is influenced by the electric conductivity, which is equivalent to a resistance with a great numerical value, and the integral potential is uniformly and linearly distributed. In the converter valve, a water pipe becomes a pressure equalizing means which is very convenient to adopt; the water path clamping method is characterized in that a connection point with a metal part of an insulator string is additionally arranged on a water pipe, and a natural voltage division result of a stray capacitor is influenced through a large resistance and a uniform linear voltage distribution characteristic of a water path, so that the purpose of voltage balance is achieved;
three types of stray capacitors C are formed by the metal part provided with the insulator string and the surrounding conductors1、C2And C3(as shown in FIG. 1); wherein C is1Is the stray capacitance between the shield, the valve module and the middle layer metal, C2Is the stray capacitance between the middle layer metal and the grounding base C3Is the stray capacitance between the shield, the valve module and the grounded base. The potential distribution on the insulator string is uneven due to the difference between the existence of the three stray capacitances and the numerical value;
the waterway before clamping can be equivalent to a resistance poleLarge resistances R, and C1、C2、C3The equivalent circuit relationship (as shown in fig. 2) is that after a clamping point connected with the metal part of the insulator is added on the water pipe, the equivalent circuit relationship is R1Is a resistance, R, at the upper section of the clamping point of the water path2Is the resistance at the lower section of the waterway clamping point (the circuit diagram is shown as a in figure 3); the valve tower model is equivalent to two capacitors connected in series and two resistors connected in series, and then the two groups of components are connected in parallel (the circuit diagram is shown as b in fig. 3); the potential of the water path is linearly distributed under the current field, the resistance value of the water path is smaller than the reactance value of the capacitor, and the clamping point can be changed
And
more closely, the voltage distribution is uniform, and then the problem of uneven voltage distribution caused by stray capacitance is effectively solved by water path clamping;
the method comprises the two steps of selecting the waterway clamping point and calculating the optimization effect. The position of the clamping point can be selected repeatedly, and the optimal clamping point position is selected. The optimization effect calculation can adopt various methods, and currently, the method generally adopts finite element electric field calculation. In the invention, the coupling of the current field and the electrostatic field after the waterway clamping is considered, the valve model becomes a quasi-static electric field model, the difficulty of directly analyzing the quasi-static electric field is higher, the realization in ANSYS software is more difficult, and in order to obtain a better optimization effect, a circuit equivalent calculation method is adopted to calculate the optimization result, so that the engineering requirements of repeatedly modifying the clamping point position and searching for an optimal optimization scheme are more suitable. The circuit parameter calculation is carried out through the equivalent resistance capacitance value, the calculation is simple, the calculation time is short, and the engineering cost and time can be greatly saved. The main equalization process is as follows:
the voltage distribution of two series insulators under the alternating current and direct current withstand voltage test of a certain converter valve of +/-800 kV as shown in FIG. 4 is optimized as an example.
The voltage distribution results of the two series insulators before optimization are obtained through ANSYS finite element electric field calculation, the voltage division percentage of the upper-layer insulator is 64.6%, and the voltage division percentage of the lower-layer insulator is 35.4%.
Step 1: and increasing the waterway clamping point at a proper height for optimization.
Considering the installation convenience, firstly, a potential clamping point is added at the position of the insulator series middle hardware cross beam and the water pipe with the same horizontal height, and the potential clamping point is determined as the No. 1 clamping point.
Step 2: and calculating the optimized voltage distribution condition. The calculation method includes, but is not limited to, finite element electric field calculation and circuit equivalent calculation, and the circuit equivalent calculation is adopted in the embodiment.
Three types of stray capacitors C are formed by the metal part provided with the insulator string and the surrounding conductors1、C2And C3(as shown in FIG. 1); wherein C is1Is the stray capacitance between the shield, the valve module and the middle layer metal, C2Is the stray capacitance between the middle layer metal and the grounding base C3Is the stray capacitance between the shield, the valve module and the grounded base. The potential distribution on the insulator string is uneven due to the difference between the existence of the three stray capacitances and the numerical value;
as shown in fig. 4, the bottom layer valve module and the valve bottom grading ring are first layer conductors corresponding to the number 1 in fig. 1; the middle layer flange is a second layer conductor which is numbered as 2 in the corresponding figure 1; the bottom grading ring, the base and the ground map 1 form a third layer of conductor, which corresponds to the number 3 in the map 1, and the circuit equivalent relation is shown in the map 1; the water path before clamping can be equivalent to a resistor R with extremely large resistance value and a resistor C1、C2、C3Is shown in FIG. 2, wherein C1Is the mutual capacitance between equivalent cell No. 1 and equivalent cell No. 2, C2Is the mutual capacitance between equivalent cell No. 2 and equivalent cell No. 3; after a clamping point connected with the metal part of the insulator is added on the water pipe, the circuit is equivalent as shown in figure 3, R1Is a resistance, R, at the upper section of the clamping point of the water path2Is the resistance of the lower section of the waterway clamping point; the valve tower model is equivalent to two capacitors connected in series and two resistors connected in series, and then the two capacitors and the two resistors are connected in seriesThe components are connected in parallel; taking into account the capacitance C between the valve module and the intermediate flange of the series insulator1And the middle flange to ground capacitor C2The difference between them is the main cause of the voltage distribution imbalance. In this example, capacitance extraction is performed in units of layers, considering that the conductor potentials of each layer are equal. And establishing a three-dimensional model of the converter valve shielding system by adopting ANSYS, subdividing the three-dimensional model, and extracting equivalent parasitic capacitance parameters based on a finite element method. The phenomenon of uneven voltage division of the original capacitor is improved. Calculate the known C1＝41.18pF， C285 pF. Water route fluid conductivity of 2.86 × 10-5S/M (namely the resistivity rho is 3.5M omega cm), when the waterway clamping point is positioned at the position of the horizontal height of the hardware cross beam in the middle part of the serial connection with the insulator, R is1＝67.95MΩ、R254.98M Ω. The voltage distribution ratio after installation of clamp point No. 1 is obtained by calculation and is shown in table 1.
Voltage distribution result after clamp point clamp of No. 11 in table
And step 3: repeatedly modifying the position of the clamping point according to the engineering requirements and searching the optimal optimization result
In this example, the position of the clamping point of the waterway was repeatedly modified, and as shown in FIG. 5, the position of the clamping point was continuously moved upward from the position of the No. 1 clamping point (length of one bend: 1.178m), and the description of the position of the clamping point was as shown in Table 2, and different clamping points and potential distributions were obtained as shown in Table 2.
TABLE 2 different Voltage distribution results for different clamped points
Considering that the voltage distribution condition of the series insulator is mainly influenced by the resistance of the water path in the direct-current withstand voltage test, the selection of the clamping point position can correspondingly change the voltage distribution condition of the series insulator in the direct-current withstand voltage test. In the engineering, the voltage distribution condition under the AC/DC withstand voltage test must be considered at the same time. The curve of the lower-layer insulator partial pressure percentage corresponding to different clamping points under the alternating current and direct current withstand voltage is shown in fig. 6, the flashover problem on the surface of the insulator is considered, the creep distance under the alternating current and direct current is checked for different clamping points, 4 clamping points all meet the creep distance requirement, and the flashover cannot occur under the alternating current and direct current test voltage, so that the 4 clamping points can meet the engineering voltage-sharing requirement.
Compared with the existing calculation method, the method has the following advantages:
firstly, the waterway clamping method provided by the invention can directly and quickly improve the phenomenon of potential uneven distribution caused by uneven distribution of stray capacitance by the characteristics that the waterway potential is uniformly distributed and the resistance value of the waterway is smaller than the reactance value of the capacitor through the potential clamping, the principle is simple and easy to understand, the structural characteristics of the waterway are well utilized, an additional structure is not required to be added, the engineering requirement can be well met, the installation cost is low, and the engineering implementation is convenient.
Secondly, the calculation method adopted by the invention is simple and rapid, compared with other methods, the model is not required to be repeatedly modified, a large amount of finite element calculation is carried out, the clamping point position can be repeatedly adjusted through simple parameter calculation to obtain the optimal clamping point position, the required pressure equalizing effect is achieved, the engineering difficulty is small, the calculation time is short, and the engineering cost and time are greatly saved.
Claims (2)
1. A high-voltage flexible direct current converter valve supporting insulator series voltage balancing method is characterized in that while the voltage class of a flexible direct current transmission technology based on a voltage source converter is continuously improved from +/-30 kV to +/-800 kV, the structure of a converter valve is greatly changed, insulators playing supporting and insulating roles have higher working voltage, a single insulator support cannot meet engineering requirements, and only a plurality of insulators are connected by simple machinery to form an insulator string to solve the problem; actually, a plurality of insulator strings are arranged in a converter valve tower to enter and exit a cooling water pipe, the electric conductivity of the insulator strings influences the potential distribution in the converter valve tower, and the potential distribution is equivalent to a resistor with a large value, so that the whole potential is uniformly and linearly distributed; in the converter valve, a water pipe becomes a pressure equalizing means; the water path clamping method is characterized in that a connecting point with a metal part of an insulator string is added on a water pipe, the voltage distribution on the insulator string is subjected to circuit equivalence by using the self large resistance of the water path and stray capacitance, and the voltage distribution on the insulator string obtains a result through circuit equivalence calculation; the method specifically comprises the following steps:
step 1: a connecting point with a metal part of the insulator string is added at a proper position of the water pipe, and a natural voltage division result of the stray capacitor is influenced through the large resistance and the uniform linear voltage distribution characteristic of the water channel;
step 2: calculating the optimized voltage distribution condition by adopting a circuit equivalent calculation method; the method comprises the following steps: three types of stray capacitors C are formed by the metal part provided with the insulator string and the surrounding conductors1、C2And C3(ii) a Wherein C is1Is the stray capacitance between the shield, the valve module and the middle layer metal, C2Is the stray capacitance between the middle layer metal and the grounding base C3Is the stray capacitance between the shield, the valve module and the grounded base; the water path before clamping can be equivalent to a resistor R with large resistance, and after a clamping point connected with the insulator metal part is added on the water path, the circuit is equivalent to R1Is a resistance, R, at the upper section of the clamping point of the water path2Is the resistance of the lower section of the waterway clamping point; the valve tower model is equivalent to two capacitors connected in series and two resistors connected in series, and then the two groups of components are connected in parallel; the potential of the water path is linearly distributed under the current field, the resistance value of the water path is smaller than the reactance value of the capacitor, and the clamping point can be changed
More closely, the voltage distribution is uniform, and the problem of uneven voltage distribution caused by stray capacitance is solved by water path clamping; the water pipe is distributed according to the resistance under the current field, affects the partial pressure with the combined action of the capacitance, and is calculated according to the formula (1-1),
R＝L/(γ×A) (1-1)
wherein:
l: the length of the water pipe;
γ: the electrical conductivity of the water;
a: the cross-sectional area of the water tube;
and step 3: and under the condition that the optimization result is not ideal, repeatedly modifying the position of the clamping point according to the engineering requirement, searching the optimal clamping point, and repeatedly calculating to obtain the optimal optimization result.
2. The method for balancing the series voltage of the high-voltage flexible direct current converter valve supporting insulator according to claim 1, wherein the circuit equivalent calculation process is as follows:
step 1: establishing a three-dimensional model of the converter valve shielding system by adopting ANSYS software, subdividing the model, and extracting stray capacitance parameters based on a circuit equivalent calculation method; obtaining the electrostatic energy of the whole valve hall through the numerical calculation function of ANSYS, thereby obtaining the stray capacitance of each part; after obtaining each circuit parameter, the valve tower model is equivalent to a plurality of capacitors connected in series and a plurality of resistors connected in series, and then the two component devices are connected in parallel, so that the voltage distribution result of the series insulator after the water path clamping is obtained;
step 2: according to a waterway resistance calculation formula and the actual waterway clamping point position, calculating the waterway resistance value of each section after the clamping point is divided;
and step 3: calculating by combining a circuit, wherein a plurality of stray capacitors are connected in series and then connected in parallel with a plurality of water path resistors to obtain the voltage division percentage;
and 4, step 4: and obtaining the actual voltage distribution condition on each insulator according to the applied voltage grade and the voltage division percentage, and judging whether the engineering requirements are met.
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| ±1100 kV 特高压直流换流阀绝缘型式试验下的电场仿真及优化;齐磊 等;《高电压技术》;20150430;第41卷(第4期);第1262-1271页 * |
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| Quantitative Analysis of Voltage Distribution within ±1100kV HVDC Converter Valve Tower under Various Transient Over-Voltage Conditions;Chen-long Liu 等;《2014 International Conference on Lightning Protection》;20141204;第1558-1564页 * |
| 高压直流换流阀用绝缘子表面电场计算及均压环设计;王星星 等;《电网技术》;20140205;第38卷(第2期);第289-296页 * |
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| CN107194102A (en) | 2017-09-22 |
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